At the start of his training Naruto finds some difficulty making the ratio of black and white chakra 8:2. Despite the fact he has a chakra shroud while practising the technique, Naruto's hands are shown to be injured as he practices. He asks Killer B to watch and tell him when he has got the ratio right so he can remember the feel of the technique.

Naruto has also noted that this new Rasengan is quite heavy, as he can barely hold it up. This is likely because of the Nine-Tails' chakra, which has been described as very dense in previous instances.[1][2] According to Killer B, he has almost perfected it, and the best way to learn and master it was from real-life experience on the battlefield.[3] Later during the Fourth Shinobi World War, after gaining Kurama's cooperation, Naruto gained the ability to use the Tailed Beast Ball, and subsequently, developed the Super Mini-Tailed Beast Ball, leaving the completion of this technique unnecessary.[4]

In the anime exclusive Chikara Arc, Naruto managed to create an incomplete Tailed Beast Rasengan (before he had absolute control of the Nine-Tails' chakra) which was able to petrify his Nine-Tailed clone.[5]

Trivia

The positive and negative chakra are coloured differently in the anime, with red for negative and blue for positive.[6]